Process for molding objects from rapid-setting polyurethane compositions

ABSTRACT

Molded polyurethane objects are prepared from rapid-setting polyurethane compositions employing molds prepared from foamed polymers of vinyl aromatic compounds. The molds retain their shape and dimensions sufficiently for the polyurethane composition to solidify and then the mold distorts and shrinks away from the molded object.

United States Patent [191 Kropscott et al.

[ Jan. 29, 1974 PROCESS FOR MOLDING OBJECTS FROM RAPID-SETTINGPOLYURETHANE COMPOSITIONS [75] Inventors: Earle L. Kropscott; Gerald R.

Wittenbach, both of Lake Jackson, Tex.

[73] Assignee: The Dow Chemical Company,

Midland, Mich.

[22] Filed: June 19, 1972 [21] Appl. No; 264,058

[52] US. Cl 264/219, 264/317, 264/318, 264/337, 264/DIG. 44

[51] Int. Cl. B29c l/02, B29c 1/08 [58] Field of Search 264/317,337-338, 264/313, DIG. 44, 221-225, 318, 321, 334,

331, 219; 249/134; 260/25 BC, 2.5 BD

[56] References Cited UNITED STATES PATENTS 3,378,511 4/1968 Newton260/3l.8 N

3,515,779 6/1970 Jones 249/134 2,722,719 11/1955 A1tstadter..... 264/3213,632,724 1/1972 Hilgeman, Jr 264/228 Primary Examiner-Robert F. WhiteAssistant Examiner-Gene Auville Attorney, Agent, or Firm-William M.Yates et a1.

[ ABSTRACT 8 Claims, No Drawings The present invention relates to aprocess for preparing molded objects from rapid-setting polyurethanecompositions.

Polyurethane molded objects are usually prepared employing moldsconstructed of wood, metal, nonfoamed thermoplastic such as polyethyleneor polypropylene, reinforced thermoset resins such as glass reinforcedepoxy resins and the like. However, component parts or objects havingintricate shapes and undercuttings must usually be machined because theycannot be readily removed from a mold.

It has now been discovered that polyurethane objects having intricate orcomplicated designs or configurations can be prepared from rapid-settingpolyurethane foam employing molds constructed of foamed vinyl aromaticpolymers and copolymers.

These molds possess the ability to retain their shape for a timesufficient for the rapid-setting polyurethane compositions to rapidlysolidify, i.e. within a period of from about 20 seconds to about minutesand preferably from about 30 seconds to about 100 seconds. Then, as theheat continues to build up within the polyurethane composition, suchheat is sufficiently transferred to the foamed vinyl aromatic polymermold such that the mold shrinks away from the solidified cast or moldedobject. By this time, the molded article has achieved a sufficientstrength to maintain its shape.

Suitable mold materials include the foamed polymers of such vinylaromatic compounds as those represented by the formula wherein each Rand R are, independently, hydrogen, an alkyl or haloalkyl group havingfrom one to about four carbon atoms, or a halogen atom includingpolymers of such compounds as styrene, methyl styrene, chlorostyrene,chloromethylstyrene, ethyl styrene, butylstyrene, propyl styrene,bromostyrene, bromomethyl styrene, mixtures thereof and the like.

Also included are copolymers of any of the above mentioned vinylaromatic compounds or mixtures thereof with such vinyl monomers asacrylonitrile, methyl methacrylate, methacrylonitrile, butyl acrylate,2-ethylhexyl acrylate, mixtures thereof and the like.

Particularly suitable mold materials for use in the process of thepresent invention include foamed copolymers comprising a majorproportion, of a vinyl aromatic compound or mixture of such compoundswith a minor proportion of a vinyl monomer, or mixture of such monomers.

Any polyurethane composition which rapidly solidifies without theapplication of any external source of heat and possesses the ability ofmaintaining its shape without any means of external support within aperiod of about 5 minutes and preferably within a period of about 3minutes or less. Such times are measured from the time all of thecomponents are mixed together wherein the catalyst is usually the lastcomponent to be added.

The particular composition of the polyurethane is not significant solong as it rapidlysolidifies and possesses the above mentionedrequirement to hold its shape after an elapse of the times previouslydescribed.

Suitable polyurethane compositions from which objects can be molded bythe process of the present invention include those of US. Pat. No.3,378,511 and coassigned, copending applications NON- ELASTOMERICPOLYURETHANE COMPOSI- TIONS by F. Olstowski and D. B. Parrish, Ser. No.179,149 filed Sept. 9, 1971, now abandoned; RAPID- SETTING POLYURETHANEELASTOMER COM- POSITIONS by D. B. Parrish and F. Olstowski, Ser. No.191,344, filed Oct. 21, 1971, now U. S. Pat. No. 3,725,355; RIGIDPOLYURETHANE COMPOSI- TIONS by F. Olstowski and D. B. Parrish, Ser. No.191,343, filed Oct. 21, 1971, now U. S. Pat. No. 3,746,692;RAPID-SETTING POLYURETHANE COMPOSITIONS by E. E. Jones, F. Olstowski andD. B. Parrish, Ser. No. 195,498, filed Nov. 3, 1971, now U. S. Pat. No.3,726,827; RAPID SETTING POLY- URETHANES FROM DIOLS AND POLYFUNC- TIONALISOCYANATES by F. Olstowski, Ser. No. 205,697, filed Dec. 7, 1971, nowabandoned; SOLID, RAPID-SETTING, RIGID POLYURETHANES, by F. Olstowski,Ser. No. 221,784, filed Jan. 28, 1972, now abandoned; FLUIDRAPID-SETTING URE- THANE COMPOSITIONS by F. Olstowski and D. B. Parrish,Ser. No. 246,903, filed Apr. 24, 1972; POLY- URETHANE FOAMS BLOWN WITHWATER VA- POR by F. Olstowski, Ser. No. 246,922, filed Apr. 24, 1972;and POLYURETHANE FOAMS FROM SOLID FOAMING AGENT by F. Olstowski and D.B. Parrish, Ser. no. 247,030, filed Apr. 24, 1972.

The following examples are illustrative of the present invention but arenot to be construed as to limiting the scope thereof in any manner.

The following definitions apply to the components employed in thefollowing examples.

Polyol A was the reaction product of glycerine with propylene oxide in amolar ratio of about 1:3, respectively and having a molecular weight ofabout 260.

Prepolymer A was the reaction product of Polyol A with an excess of an/20 mixture of 2,4- and 2,6- toluene diisocyanate and having about 30%free NCO by weight.

EXAMPLE I A mixture consisting of 2830 grams of Prepolymer A 2270 gramsof dioctyl phthalate c 1707 grams of Polyol A was prepared to which wasadded and mixed 17 grams of stannous octoate catalyst. The resultantmixture was then poured into an open polystyrene foam mold having a wallthickness of about 1 7% inches and a cavity in the general configurationof a pump base having the dimensions 29 X 12 X 3 k inch. Within about 30seconds after catalyst addition, the mixture suddenly solidified andwithin 5 minutes after catalyst addition the mold shrank away from therigid polyurethane casting which maintained the general configuration ofthe mold cavity.

EXAMPLE 2 A mixture consisting of 408 grams of Prepolymer A 326 grams ofdioctyl phthalate 246 grams of Polyol A was prepared to which was addedand mixed 2.5 grams of stannous octoate catalyst. The resultant mixturewas then poured into and around a polystyrene foam mold having a wallthickness of about 56 inch and a cavity in the general configuration ofa drinking cup having the approximate dimensions of 3 A inch high, topdiameter of 2 inches and bottom diameter of 2 inches, suspended in apaperboard container about inches high, a top diameter of about 4 inchesand a bottom diameter of about 4 inches. Within about 30 seconds aftercatalyst addition, the mixture suddenly solidified and within 5 minutesafter catalyst addition the mold shrank away from the rigid polyurethanewhich maintained the general configuration of the mold cavity. Thedrinking cup was reduced to droplets of beads which clung to the sidesof the molded objects. The droplets were easily removed by a slightbrushing motion.

EXAMPLE 3 A mixture consisting of 146 grams of Prepolymer A l 17 gramsof dioctyl phthalate 87.8 grams of Polyol A was prepared to which wasadded and mixed 0.9 grams of stannous octoate catalyst. The resultantmixture was then poured around a polystyrene foam cube having adimension on each side of about 1% inches, a density of about 6 lb./ftwhich was suspended in a paperboard container about 5 inches high, a topdiameter of about 4 inches and a bottom diameter of about 4 inches.Within about 30 seconds after catalyst addition, the mixture suddenlysolidified and, within 5 minutes after catalyst addition the mold shrankaway from the rigid polyurethane which maintained the generalconfiguration of the mold and upon cutting the cast object through thecenter, the l /2 inches polystyrene foam cube had shrunk to about '75 XW4 inch while the cavity in the cast object was about l X 1 X l 1%inches.

EXAMPLE 4 A mixture consisting of 542 grams of Prepolymer A 433 grams ofdioctyl phthalate 326 grams of Polyol A was prepared to which was addedand mixed 3.3 grams of stannous octoate catalyst. The resultant mixturewas then pumped into the bottom of a polystyrene foam mold having a wallthickness of about l inches and a cavity in the general configuration ofa grating. The mold cavity was prepared by sawing 3/16 X 1 inch groovesin a polystyrene foam board. The ends and top were made from apolystyrene foam block. Within about 30 seconds after catalyst addition,the mixture suddenly solidified and within 5 minutes after catalystaddition the mold shrank away from the rigid polyurethane whichmaintained the general configuration of the mold cavity.

EXAMPLE 5 A mixture consisting of 164 grams of prepolymer a 1 17 gramsof dioctyl phthalate 87.8 grams of Polyol A was prepared to which wasadded and mixed 0.9 grams of stannous octoate catalyst. The resultantmixture was then poured around a 63% styrene, 27% acrylonitrilecopolymer foam cube having a dimension of each side of about 1 36 incheswhich was suspended in a paperboard container about 5 inches high, a topdiameter of about 4 1% inches and a bottom diameter of about 4 inches.Within about 30 seconds after catalyst addition, the mixture suddenlysolidified and within 5 minutes after catalyst addition the mold shrankaway from the rigid polyurethane which maintained the generalconfiguration of the mold and upon cutting the cast object through thecenter, the l inches foam cube had shrunk to about 1 X l X inches whilethe cavity in the cast object was about 1 X l X l inches.

We claim:

1. A process for the preparation of molded polyurethane objects whichcomprises A. preparing a mold of the desired configuration from a foamedpolymer of a vinyl'aromatic compound;

B. filling the mold with a rapid-setting polyurethane composition,allowing said composition to rapidly solidify so as to maintain theshape provided by said mold without any external source of heat and anyexternal support means within a period of less than about 5 minutes andcausing the mold to distort and shrink away from the solidified objectdue to heat from the exothermic reaction of the polyurethane formation;

C. removing the molded object from the remaining portion of the mold.

2. The process of claim 2 wherein said polyurethane composition rapidlysolidifies and maintains the shape provided by the mold within less thanabout 3 minutes.

3. The process of claim 1 wherein the vinyl aromatic compound is acompound represented by the formula CH=CH1 wherein each R, and R areindependently, hydrogen, alkyl or haloalkyl groups having from one toabout four carbon atoms or a halogen atom.

4. The process of claim 3 wherein said polymer is a copolymer of any twoor more of such vinyl aromatic compounds.

5. The process of claim 3 wherein said polymer is polystyrene.

6. The process of claim 3 wherein said polymer is a copolymer comprisingin major proportion a vinyl aromatic compound or mixture of vinylaromatic compounds and a minor portion of a vinyl monomer or mixture ofvinyl monomers.

7. The process of claim 6 wherein said vinyl monomer is acrylonitrileand the vinyl aromatic compound is styrene.

8. The process of claim 7 wherein said polymer comprises 27%acrylonitrile and 63% styrene.

@33 3 V -UNITED STATES PATENT OFFICE CERTIFICATE .OF CORRECTIONInventor(s) Earle L. Kropscott and Gerald R. Wittenbach It is certifiedthat; error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Col. 2- l. 56, delete "c" Col. 3, 1.; 46, change "1/2 x 3/4" to read--l/2 x 3/4 x 3/4-.

Col. 4, l. 37, change "Claim 2" to read --Claim l--.

Signedand sealed this 10th day of December 1974.

" (SEAL) ;;!Attest:

' McCOY M. GIBSON JR'. 0. MARSHALL DANN Attesting Officer Commissionerof Patents

2. The process of claim 2 wherein said polyurethane composition rapidlysolidifies and maintains the shape provided by the mold within less thanabout 3 minutes.
 3. The process of claim 1 wherein the vinyl aromaticcompound is a compound represented by the formula
 4. The process ofclaim 3 wherein said polymer is a copolymer of any two or more of suchvinyl aromatic compounds.
 5. The process of claim 3 wherein said polymeris polystyrene.
 6. The process of claim 3 wherein said polymer is acopolymer comprising in major proportion a vinyl aromatic compound ormixture of vinyl aromatic compounds and a minor portion of a vinylmonomer or mixture of vinyl monomers.
 7. The process of claim 6 whereinsaid vinyl monomer is acrylonitrile and the vinyl aromatic compound isstyrene.
 8. The process of claim 7 wherein said polymer comprises 27%acrylonitrile and 63% styrene.